Read-in mechanism for settable type wheels



Feb. 2, 1965 R. J. JABLONSKI 3,168,035

READ-IN MECHANISM FOR SETTABLE TYPE WHEELS Filed Dec. 28, 1961 4 Sheets-Sheet 1 N P: E.

INVENTOR. RICHARD J. JABLONSKI.

A T TORNE Y.

Feb. 2, 1965 R. J. JABLONSKI READ-IN MECHANISM FOR SETTABLE TYPE WHEELS Filed Dec. 28, 1961 4 Sheets-Sheet 2 INVENTOR. RICHARD J. JABL ONSKI.

@K ATTORNEY.

Feb. 2, 1965 R. J. JABLONSKI 3,168,035

READ-IN MECHANISM FOR SETTABLE TYPE WHEELS Filed Dec. 28, 1961 4 Sheets-Sheet 3 Fig 10. 76 85 mo 22 6| 6 4 f 63 78 09-.6 74

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66 63 65 62 I18 ISO s;

INVENTOR.

RICHARD J. JABLONSKI.

ATTORNEY.

R. J. JABLONSKI READ-IN MECHANISM FOR SETTABLE TYPE WHEELS Filed Dec. 28, 1961 Feb. 2, 1965 4 Sheets-Sheet 4 I76 ee 65 I80 6 we 7 I 0 a i W I 2 l m w 16 2 W o 4 b O O w 4 8 v b A 9/ A /3 H b 2 my W TN N0 E W8 0 I W 8 W H 0., M M 1v H o F m n R A United States Patent ()1 3,168,035 READ-IN MCEEIHANISM FOR SETTABLE TYPE WHEELS Richard J. Jablonski, Detroit, Mich., assignor to Burroughs Corporation, Detroit, Mich., a corporation of Michigan Filed Dec. 28, 1961, Ser. No. 162,749 3 Claims. (Cl. 101-110) This invention relates generally to printing apparatus of the type having rotatable print wheels and particularly to mechanism for stopping rotation of the print wheels to position selected print elements thereon relative to a print line.

It is an object of the present invention to provide for printing apparatus of the type having a rotatable print Wheel and a control member thereof to control the stopping and positioning of the print wheel relative to a printing line, an improved read-in mechanism interconnecting the wheel and the control member including a stop member biased to rapidly move into engagement with and stop the wheel without such rebounding action of the said stop member as would allow the wheel to rotate past the desired stopping point.

Another object of the invention is to provide for the automatic latching of the wheel stopping member in its holding position.

Another object of the invention resides in the controlling of the latching function in accordance with operation of the wheel stopping member.

Other objects of the invention will become apparent from the following detailed description, taken in connection with the accompanying drawings in which:

FIG. 1 is a fragmentary plan view of a printing apparatus embodying features of my invention;

FIG. 2 is a vertical sectional view partly in elevation, taken along the line 22 of FIG. 1;

FIG. 3 is a perspective view of certain of the mechanism of the apparatus;

FIG. 4 is an enlarged fragmentary detail View;

FIG. 5 is a vertical sectional view partly in elevation, taken along the line 55 of FIG. 1;

FIG. 6 is a vertical sectional view, taken along the line 66 of FIG. 5;

FIG. 7 is a vertical cross sectional view, taken along the line 77 of FIG. 5;

FIG. 8 is a vertical cross sectional view, taken along the line 88 of FIG. 6;

FIG. 9 is a fragmentary detail view in elevation of one of the print wheels, and

FIG. 10 is a diagrammatic illustration of the apparatus and its control system.

Referring to the drawings by characters of reference, the printing apparatus includes a bank of print wheels 10 mounted to rotate individually and freely on a fixed shaft 12 that extends horizontally between and is supported on a pair of spaced apart upright supporting plates 14 of which only one is shown. The print wheels 10 respectively represent the different ones of the denominations of the decimal system. Each of the print wheels 10 has a number of radially and equally spaced teeth 16, there being eleven of such teeth on each wheel of the present printer. 0n the ends of ten of the teeth 16 are provided printing elements corresponding to the numeric digits 0-9 inclusive, the end of the eleventh tooth, designated by the numeral 18, being a blank or without a printing element in the present system and normally being disposed at the print line of the printing apparatus.

In mesh respectively with the print wheels 10 are read-in wheels 20 which are preferably larger in diame- 3,168,035 Patented Feb. 2, 1965 ice ter than the diameters of the print wheels 10, the ratio being 2 to l in the present apparatus. The read-in wheels 20 are individually mounted on a driven shaft 22 which is in turn mounted for rotation on the side plates 14 and on similar outwardly spaced side plates 24 of which only one is shown. Each of the read-in wheels 20 is normally and individually coupled to the shaft 22 by a slip clutch 25 which includes a hub-like clutch member 26 which is fixed onto the driven shaft 22 by a pin 28, as shown in FIG. 6. The read-in wheel 20 has a hub 30 to receive an end portion of reduced diameter of the clutch member 26, the read-in wheel being retained on the clutch member 26 by a collar 31, fixed onto shaft 22. The clutch member 26 has a radially extending bore wherein an outwardly urged spring pressed detent or ball 32 normally clutches the read-in Wheel 20 to the driven shaft 22. The ball detent 32 is adapted to engage alternately in a pair of V-shaped diametrically disposed recesses 34 in the read-in wheel hub 30, such recesses being necessary as the present apparatus requires half cycles of operation of the read-in wheel shaft 22.

A normally disengaged clutch mechanism 36 is provided for effecting half cycles of operation of the driven shaft 22 and comprises, in general, a clutch driving component 38 and a driven clutch component 40. The clutch components 38 and 40 are mounted on the shaft 22, the driven component 40 being fixed to the shaft and the driving component 38 being normally freely rotatable on the shaft. A continuously rotating driving shaft 42 drives the clutch component 38, such as by means of suitable gears 44, 46 and a driving belt 48, the gear 46 being integral with the clutch component 38.

Projecting laterally and externally from the driven clutch component 40 there is a clutch operating arm 50 which is biased to a position corresponding to clutch engagement and is normally held in its clutch disengaged position, shown in FIG. 1, by a stop lug 52 on a horizontal carrier or slide member 54. The slide member 54 may be slidably supported on a pair of horizontally spaced apart pins 56 mounted on and projecting laterally from the side plate 24 of the machine frame structure. A second stop lug 58 on the slide member 54 is diametrically oppositely disposed from the stop lug 52 to limit rotation of the driven clutch member to a one-half revolution. It will be apparent to those skilled in the art that when the slide member 54 is shifted to the left, facing FIG. 2, the clutch operating arm 50 will be released by lug 52 to effect engagement of the clutch component, and that the stop lug 58, as a result of the shifting of slide member 54, will be in position to be engaged by the operating arm to effect disengagement of the clutch, thus limiting the clutch to one-half cycles of rotation. A spring 60 acts to shift the slide member 54 to the left facing FIG. 2. Any suitable onehalf cycle clutch may be employed, such as the clutch shown in the patent to Thomas M. Butler, No. 2,627,333, issued February 3, 1953, for Front Feed Paper Carriage Construction for Accounting and the Like Machines. As will be hereinafter more fully understood, in Operation, when the slide member 54 is returned to its starting position shown, the driven shaft 22 is rotated another one-half revolution to return the read-in wheels 20 and thus the print wheels 10 to their home or starting positions.

Since the mechanisms of each of the denominational banks of the machine are alike, the following description is limited to one such mechanism for convenience and clarity of the description and to avoid unnecessary repetitious description. Each bank includes a retractable stop member and holder 61 for normally stopping and holding the read-in wheel 20 in home position, the stop member preferably comprising a pair of horizontally disposed parallel slide members 62 and 63 connected together 'as one member by a cross member or rod 65 having its ends secured in and to the slide members. These slide members 62, 63 are provided with elongated apertures to slidably receive fixed guide pins 64 and 66 for supporting the slide members, the pins being mounted on and. extending laterally from'one of the frame side plates 14. Normally, the retractable stop member 61 is. in a position such that one end of the member 62, as at 67, is holding the read-in wheel 20 inhome or cycle. starting position against the action of the read-in wheel slip clutch tending to rotate the wheel. Fixed to and projecting laterally from one side of the read-in Wheel 20 there is a pair of diametrically oppositely disposed abutment members or studs 68 and 70 of which stud 70 is normally'engaging the end of slde member 62, as shown, to prevent rotation of the read-in wheel. The stop member 61 is moved to and yieldingly held in its normal position shown 'by a coil spring 74, the spring 74 being normally restrained by an actuator or cam 76 affixed onto a cam shaft 78, which is parallel to the read-in shaft 22. In the interest of manufacturing'costs, the cam 76 is made in two parts including the cam proper 76 and an offset lug 84 which is formed on a disc 85, the disc being affixed to the shaft 78 to rotate with the cam proper. On an upstanding leg 80 of 'the slide member 62 there is an abutment mem- 'ber82 which is normally in engagement with the end of the lug 84 on cam 76 to thus provide a quick release of the stop member 61 and resultant retraction thereof by the spring 74. The abutment member 82 has a shank portion on which a roller 86 is mounted, the roller 86 being a follower for cooperation with the cam 76. Upon rotation, the cam 76, acting on the roller 86 is operable to move the stop member 61 to the left into holding relation with the read-in whee120 and then transfer the holding function to the lug 84. It will be seen that when the lug 84 moves out of holding relation with the abutment 82, the restraint of spring 74 is removed and the spring rapidly moves the stop member 61 to the right to release the read-in wheel 20. p

The cam shaft 78 is mounted for rotation on the frame side plates 14 and 24 and on this shaft there is a normally disengaged clutch device 90 which is similar to the previously described clutch device 36. The clutch 90 comprises a driving component 92 which is normally free to rotate on the cam shaft 78 and a driven component 94 which is fixed to the cam shaft 78. Projecting laterally from the clutch component 94 there is a clutch operating arm 96 which is biased to a position to effect clutch engagement and this arm is normally held in its clutch disengaged position by a lug 98 on a slidable carrier or slide member 100. The slide member 100 may be slidably mounted on a pair of horizontally spaced apart pins 102 which maybe mounted on and project laterally from the side plate 24. A spring 104 urges the slide member 100 to the left, facing FIG. 1, to position the lug 98 in the path of rotation of the clutch operating arm 96. The driving clutch component 92 may be. driven through suitable gears and a belt 106 from the drive shaft 42, as shown in FIG. 2, the gears including a gear 108 which is integral with the clutch driving component 92.

Pivotally connected to one end of the slide member 100 is an armature 110 of a solenoid 112 which operates to move the slide member to the right, facing FIG. 2 so as to disengage the stop lug '98 from the clutch operating arm 96. The solenoid 112 is momentarily energized or pulsed upon the closing of a push button switch 114. When the clutch arm 96 is released by lug 98, the cam 88 is rotated through one revolution and for substantially the first 180 of its revolution the cam allows the spring 74 to move the stop member 61 to retracted position and during the last 180 of'its revolution, the

cam returns the stop member to home position in the path of the read-in wheel pin 68.

A cam 116, fixed onto the cam shaft 78,-operates a lever 118 to trip the clutch device 36, the lever 118 being biased by a coil spring 119 to hold a cam follower roller 120 in engagement with the cam and to hold an arm 122 of the lever in engagement with a roller 124 carried by the slide member 54, as shown in FIG. 2. The arrangement is such that a dwell in cam 116 delays the tripping and thus the engagement of clutch 36 until after slide 61 has retracted to the point where the wheel engaging end 67 of slide member has cleared the Wheel abutment pin 70.

Another stop member 126 is provided to stop the readin wheel 20 during the interval when the stop member 61 is retracted, the purpose being to stop and hold the print wheel 10 with a selected one of the print elements of print wheel 10 at the print line. The stop member 126 is slidably supported on a pair of horizontally spaced apart pins 127 mounted on frame plate 14 and has a reduced end 128 which is positioned to engage between a pair of adjacent teeth of the read-in wheel 20 following release of the stop member 126. A thrust member or spring 130 urges the stop member 126 into engagement with the teeth of the read-in wheel 20 and is normally restrained by a retractable holder or cam 132 which is operatively connected tothe slide member 126 by a lever 133, the cam 1 32 being afiixed onto the camshaft 78. One arm 134 of the lever 133-carries a cam following roller 136, andranother arm 138 carries a s'tud 140 which engages a shoulder 142 formed in the top edge of the slide member-126. The lever 133 is pivotally mounted on a stub shaft '143' which in turn is mounted at one end thereof on the frame side plate 14. A biasing spring 144, connected to .an upwardly directed arm 146 of lever 133, maintains the cam follower or'roller 136 in contact with the cam 132. As clearly shown in FIG. 3, the cam 132 has a step 148 nearfwhich the roller '136'is positioned when the parts are-in their normal positions, and that on initialrotation of the cam 132, the roller moves down the step whereby the lever'133 is free to be pivoted by the spring 144 in a clockwise direction, facing FIG. 5.

Each of the :stop members 126 of each bank of mechanisms has an electrically operated holding means or latch 151 which may be the armature of a'solenoid, designated generally by the numeral 152, only the solenoid of one of the banks being shown in the drawings. The solenoid 152 includes the usual coil 154 and the armature 151, the armature spring biased to open position. A portion of the free end of the-armature-151 positions in a notch 158, provided in the lower edge of the stop member 126. Normally, the solenoid 152 is di /energized, the holding function for normally holding the stop member 126 retracted being performed by the cam 132 acting through lever 133 on the stop member in the home positions of the parts. The circuit of the solenoid coil 154 includes a diagrammatical illustration of a scanner or pulse distributor switching device comprising in general a plurality of normally closed switches 0 to 9'and a rotatable actuator 162'having acommon connecting contact-161, the distributor and solenoid being connected electrically to the output terminals of a bridge rectifier 163 connected to a power source. The actuator-1'62 is fixed to a rotatable shaft 164 which is coupled to and rotates with the read-in wheel shaft 22. *For a more detailed description of the read-in system,.reference may be had to the pending application of Irvin W. Borutzke et 'al., for Printing Apparatus rotate the read-in wheel. In order to prevent rebound of the stop member 126 and therefore resultant erroneous positioning of the read-in wheel 20, I provide a latch member 170 adapted to position behind an upstanding keeper or lug 172 on slide member 126 at about the same time that the stop member moves into engagement with the read-in wheel 20. The latch member 170 is pivoted on a pin or rod 174 which is mounted at one end thereof on the adjacent frame side plate 14. A coil spring 176, connected to one end of the latch member 170 biases the latch member to latching position, the spring being anchored at one end thereof to the side plate 14. The other end of the latch member 170 has a triangular shaped opening providing a cam 178 which is held by spring 176 against a horizontally movable cam follower or pin 180, mounted on and carried by the slide member 63. Thus, the actuator or cam 76 acting through the interconnecting slide member 63 and cam follower 180 actuates the latch member 170. It will be seen that when the slide member 63 is retracted by spring 74, the pin 180 moves away from the cam 178 which allows the spring 176 to pivot the latch member 170 counterclockwise until the latch rests on the upper end of the lug 172. With the latch member in this position, it will be seen that when the slide member 126 is thrust toward wheel 20, the latch member 170 will be immediately pivoted down behind the latch keeper or lug 172.

Operation The machine operator first indexes the number to be printed by closing the corresponding one of the row of settable switches to 9 which, for purposes of this description will be assumed to be the digit switch. The closing of the digit 5 switch causes the solenoid coil 154 to be energized, as will be seen in FIG. 10, which then attracts and holds the latch member 151 in latching position to hold the stop slide 126 in retracted position. At this time, the lach member 151, and the cam 132 through lever 146 are both holding the stop slide 126 in retracted position. The machine operator then depresses the cycle starter switch 114, shown in FIG. 1, which causes the solenoid 112 to be pulsed whereupon the solenoid moves the clutch controlling slide 100 to the right, facing FIG. 2, to release the clutch operating arm 96, followed by the return of the slide to normal position by the spring 104. The release of the clutch operating lever 96 effects coupling of the shaft '78 to the driven clutch component 92 whereby the camshaft 78 is rotated one revolution, or until the now revolving clutch operating arm 96 again abuts the stop lug 98.

On initial rotation of the camshaft 78, the lug 84 of cam 76 moves away from the abutment 82 to release the stop member 61 which is then retracted by the spring 74. Retraction of the stop member 61 moves the pin 180, carried thereby, away from the latch cam 178, thus allowing the spring 176 to pivot the free end of the latch member 170 down against the top of the lug 172. At substantially the same time that the slide member 61 is retracted, the cam 132 releases the lever 133 to pivot in a direction to release the stop slide 126 to the holding force of the electrically operated latch 151. Closely following the release of the slide member 61 by the cam 76 and the release of slide member 126 by cam 132, the cam 116, FIG. 2, allows the lever 118 to be pivoted by spring 119 which in turn allows the spring 60 to move the shifter plate 54 to the left. Movement of the shifter plate 54 to the left releases the clutch operating arm 50 which allows the clutch to engage and rotate the read-in shaft 22 and also places the stop lug 58 in position to intercept and actuate the arm 50 so as to limit rotation of shaft 22 to a one-half revolution.

The read-in wheel 20, through its slip clutch connection 25, rotates with the shaft 22 and when the distributor switch actuator 162 of FIG. 10, which is coupled to rotate with shaft 22, opens the 5 switch, the solenoid 154 is de-energized, releasing the stop slide 126 which is then thrust against the toothed read-in wheel 20 by spring 130 to stop the wheel with the 5 printing element at the print line. When the stop member 126 moves into engagement with the read-in wheel 20, the latch member drops off the lug 172 and is forced down behind the lug by the spring 176, as shown for example, in FIG. 4, to prevent rebound of the stop member 126. A dwell on cam 132 allows the stop slide 126 to remain in bolding relation with the read-in wheel 20 for an interval during which the printing operation takes place. As the one revolution camshaft 78 continues to rotate, a rise on the cam 88, acting on the cam follower 86, returns the stop slide 61 to normal position and at about the same time, the cam 132, acting through the lever 133 retracts the stop slide 126. Following movement of the stop member 61 to its normal position by cam 76, and the retraction of stop member 126 to its normal position by cam 132, the cam follower 120, FIG. 2, rides up on the high surface of the cam 116 as the camshaft i8 is completing its cycle of rotation and causes the shifter member 54 to be again shifted to the right, facing FIG. 2. It will be remembered that the read-in shaft 22 had completed a one-half revolution for the purpose of reading into the wheel the selected 5 digit and that the clutch operating arm 50 was thereafter being held inactive by the shifter lug 58. As a consequence, when the shifter member 54 is shifted to the right, near the completion of the one revolution of camshaft 78, the clutch 36 is tripped to effect the second one-half revolution of the read-in shaft 22. When this occurs, the read-in wheel 20, through its slip clutch, is rotated until the abutment pin strikes the end 67 of the stop slide 61. Thus, during the first onehalf revolution of the shaft 22, the read-in wheel 20 is stopped to present the selected digit of the print wheel 10 to the print line, and during the second one-half revolution of the shaft 22, the read-in wheel and consequently the print wheel 10 are restored to their normal positions.

What I claim is:

1. In a print wheel positioning apparatus having a rotatable print wheel to be stopped in a position with a selected one of a plurality of print elements thereof at a print line, a toothed read-in wheel to drive the print wheel and having a slip clutch drive connection, a scanner switch rotatable with said read-in wheel to successively open a plurality of switches representative respectively of different possible positions of said read-in wheel, a retractable stop member normally in a position blocking rotation of said read-in wheel, a spring connected to said stop member to retract said stop member, a second stop member mounted for movement into engagement with said read-in wheel between a pair of the teeth thereof to stop said read-in wheel, a spring connected to and urging said second-mentioned stop member into engagement with said read-in wheel, a rotatable cam normally in a home position holding said first-mentioned stop member in the blocking position thereof, said cam rotatable through a cycle of rotation to release said firstmentioned stop member for retraction by said spring and then return said stop member to the blocking position, a second cam rotatable with said first-mentioned cam to release said second-mentioned stop member and normally holding said second-mentioned stop member in retracted position, an electrically operated holder operable to restrain said second-mentioned stop member and electrically connected to one of said scanner switches, a latch keeper on said second-mentioned stop member, a latch member biased to latch engagement with said keeper, and means on said first-mentioned stop member and on said latch member cooperable to control operation of the latter.

2. In a print wheel positioning apparatus having a rotatable print wheel to be stopped in a position with a selected one of a plurality of print elements thereof at a print line, a toothed read-in wheel to drive the print wheel and having a slip clutch drive connection, a scanner switchrotatable with said read-in wheel to successively actuate a plurality of switches representative respectively of different possible positions of said read-in wheel, a first retractable stop member normally in a position blocking rotation of said read-in wheel and biased to retracted position, a second retractable stop member biased for movement into engagement with said read-in wheel between a pair of the teeth thereof to stop said read-in wheel, a rotatable cam normally in a home position holding said first stop member in the blocking position thereof, said cam rotatable through a cycle of rotation to release said first stop member for retraction and then return said first stop member to the blocking position, a second cam rotatable with said first cam to release said second stop member and normally holding said second stop member in retracted position, an

electrically operated holder operable to restrain said second stop member and electrically connected to one of said scanner switches, a latch keeper on said second stop member, alatch member biased to latch engagement with said keeper, and cam means on said first stop member and on said latch member cooperable to control operation of the latter in relation to said keeper.

3. In an information read-in apparatus, a read-in wheel having radially spaced extended portions about the periphery thereof representative of the digits of the decimal system and having a slip clutch drive connection, a'

system, a first retractable stop member normally in a position blocking rotation of said read-in wheel and biased to retracted position, a second retractable stop member biased for movement into engagement with said read-in wheel. between adjacent ones of a pair of said extended portions to stop said read-in wheel, a first r0- tatable cam normally in a home postion holding said first stop member in the blocking position thereof, said cam rotatable through a cycle of rotation to release said first stop member for retraction and then return said first stop member to the blocking position, a second cam rotatable with said first'cam to release said second stop member and normally holding said second stop member in retracted position, an electrically operated holder operable to restrain said second stop member after the latter is released by said second stop member and electrically connected to one of said scanner switch members, a latch keeper carried by said second stop member, a pivotal latch member biased to latch engagement with said keeper, a third cam on said-latch member, and a cam follower carried by said first stop member and cooperable with said third camrto actuate said latch member.

References Cited in the file of this patent UNITED STATES PATENTS 553,983 Heath et a1 Feb. 4, 1896 1,090,444 Barnard Mar. 17, 1914 2,569,829 Rabenda Oct. 2, 1951 2,699,857 Wales Jan. 18, 1955 2,813,608 Caburet Nov. 19, 1957 

1. IN A PRINT WHEEL POSITIONING APPARATUS HAVING A ROTATABLE PRINT WHEEL TO BE STOPPED IN A POSITION WITH A SELECTED ONE OF A PLURALITY OF PRINT ELEMENTS THEREOF AT A PRINT LINE, A TOOTHED READ-IN WHEEL TO DRIVE THE PRINT WHEEL AND HAVING A SLIP CLUTCH DRIVE CONNECTION, A SCANNER SWITCH ROTATABLE WITH SAID READ-IN WHEEL TO SUCCESSIVELY OPEN A PLURALITY OF SWITCHES REPRESENTATIVE RESPECTIVELY OF DIFFERENT POSSIBLE POSITIONS OF SAID READ-IN WHEELS, A RETRACTABLE STOP MEMBER NORMALLY IN A POSITION BLOCKING ROTATION OF SAID READ-IN WHEEL, A SPRING CONNECTED TO SAID STOP MEMBER TO RETRACT SAID STOP MEMBER, A SECOND STOP MEMBER MOUNTED FOR MOVEMENT INTO ENGAGEMENT WITH SAID READ-IN WHEEL BETWEEN A PAIR OF THE TEETH THEREOF TO STOP SAID READ-IN WHEEL A SPRING CONNECTED TO AND URGING SAID SECOND-MENTIONED STOP MEMBER INTO ENGAGEMENT WITH SAID READ-IN WHEEL, A ROTATABLE CAM NORMALLY IN A HOME POSITION HOLDING SAID FIRST-MENTIONED STOP MEMBER IN THE BLOCKING POSITION THEREOF, SAID CAM ROTATABLE THROUGH A CYCLE OF ROTATION TO RELEASE SAID FIRSTMENTIONED STOP MEMBER FOR RETRACTION BY SAID SPRING AND THEN RETURN SAID STOP MEMBER TO THE BLOCKING POSITION, A SECOND CAM ROTATABLE WITH SAID FIRST-MENTIONED CAM TO RELEASE SAID SECOND-MENTIONED STOP MEMBER AND NORMALLY HOLDING SAID SECOND-MENTIONED STOP MEMBER IN RETRACTED POSITION, AN ELECTRICALLY OPERATED HOLDER OPERABLE TO RESTRAIN SAID SECOND-MENTIONED STOP MEMBER AND ELECTRICALLY CONNECTED TO ONE OF SAID SCANNER SWITCHES, A LATCH KEEPER ON SAID SECOND-MENTIONED STOP MEMBER, A LATCH MEMBER BIASED TO LATCH ENGAGEMENT WITH SAID KEEPER, AND MEANS ON SAID FIRST-MENTIONED STOP MEMBER AND ON SAID LATCH MEMBER COOPERABLE TO CONTROL OPERATION OF THE LATTER. 